1. Field of the Invention
The invention is related to antennas, and more particularly, to reducing interference received by the antennas.
2. Description of the Related Art
Electromagnetic interference can disrupt mobile communications in both military and commercial mobile applications. This is especially true when a high-power terrestrial source is in close proximity to the mobile satellite receiver. This can be especially problematic when the mobile receiver passes fixed high-power radio sources, or perhaps even more problematic, when a military vehicle is in the presence of a radar or jamming source that is either onboard or on a nearby vehicle within the same convoy. In this case, the local interfering signal would likely overpower the weak satellite signal, even if that interfering signal were out of the frequency band of the desired signal's channel, due to non-ideal filtering. To exacerbate this problem, many of these jamming sources are ultra wideband (UWB) and consist of electromagnetic energy spread over a very large bandwidth that may overlap the frequency channel of the desired satellite signal. In this case, even the fraction of the UWB interfering power that is in-band could potentially overpower the desired satellite signal.
When a satellite receiver is subjected to such interferences, antennas can be chosen with radiation patterns that favor the direction of the satellite signal, while rejecting signals coming from known interference. However, if the direction of interference is continually changing, as in a mobile application, this fixed antenna pattern is not useful. Mechanically steered antennas are too cumbersome and slow, and the moving parts are susceptible to reliability problems. In-band filtering inside the satellite receiver is ineffective, because this in-band filtering may also filter out the desired satellite signal. Filtering in the receiver may assist with adjacent-channel interference; however, non-ideal filtering may still allow adjacent-channel interference that can render the satellite communications unusable.
Accordingly, there is a need in the art for an antenna array, which assists in reducing the above referenced interferences.